1899J MICROSCOPICAL JOURNAL. 99 



other was of a yellow tint got from oxide of manganese 

 and iron, M. Henri Cross finds that objects which to the 

 naked eye appear the same in color, look different through 

 the screen. Thus a green emerald looks a rosy violet 

 through the glass, but a false green emerald looks green. 

 True sapphire keeps its natural blue through the screen, 

 and false blue sapphire appears a rosy red. An Egyptian 

 cup of Sevres blue paste appeared blue, save a part re- 

 stored, which was red. He was able to conclude that the 

 Egyptian paste bad a base of copper blue and the restored 

 part one of cobalt. — Optical Journal. 



MICROSCOPICAL MANIPULATION. 



Spirit-Proof Micro-Cement. — Take Nelson's amber gel- 

 atine, soften with water, pour off the water, melt the gel- 

 atine with gentle heat. Add sufficient white lead in powder 

 to render it opaque. 



Focal Lengths. — It is not an easy matter to measure ac- 

 curately the focal lengths of microscopic objects ; but a 

 sufficiently close approximation can be obtained by com- 

 paring them with others, whose focal lengths are known, 

 taking care to use the same eyepiece and the same tube- 

 length. The best way of measuring the power of any 

 combination of objective and eyepiece is to place a stage- 

 micrometer on the stage and compare the graduations as 

 seen through the instrument with one eye with an ordinary 

 foot-rule, as seen at the same time with the other, both 

 eyes being open and the rule being at a distance of 10 in. — 

 A. Woolsey Blacklock, M. D. 



New Stain. — Ziemann has described a new stain for de- 

 monstrating the nucleus of the malarial parasite. He uses 

 various proportions of a one-per-cent watery solution of 

 rectified methylene blue and a one-per-cent watery solu- 

 tion of eosin. He demonstrated throughout the body of 

 the parasite certain reddish stained areas. 



To Kill Invertebrates. — Take four parts of a saturated 

 aqueous solution of corrosive sublimate and add to it one 



